Strength improvement via sprayboom application

ABSTRACT

The present disclosure provides methods and compositions for strengthening paper. The methods may include a step of spraying an anionic polymer onto a paper sheet to increase the strength of the paper sheet. The anionic polymer may have amino groups, amide groups, or a combination of amino groups and amide groups. These groups may be functionalized with an aldehyde. Methods may also include a step of adding a wet end composition to a wet end of the papermaking process.

TECHNICAL FIELD

The present disclosure generally relates to compositions and methods for manufacturing paper. More particularly, the disclosure relates to compositions and methods for increasing paper strength.

BACKGROUND

A papermaking process may include the steps of pulping wood or some other source of papermaking fibers, producing a paper mat from the pulp, the paper mat being an aqueous slurry of cellulosic fiber, depositing the slurry on a moving papermaking wire or fabric, forming a sheet from the solid components of the slurry by draining the water, pressing and drying the sheet to further remove water, and potentially rewetting the dry sheet by passing it through a size press and further drying it to form a paper product.

When conducting a papermaking process, a number of factors need to be taken into account to assure the quality of the resulting paper product. For example, when draining water from the slurry, care should be taken to retain as many fibers as possible. Additionally, the process should be carried out in a manner such that the resulting sheet has adequate strength.

Paper strength is dependent upon a number of factors, such as choice of fibers, refining methods, press loading, and chemical additives employed. Typically, paper strength additives are applied to the wet end of the paper machine, either in a thin or thick stock addition point, and often only result in a 10-15% improvement in paper strength. This strength limit is due to several factors, such as the capacity of the fiber surface to adsorb the additive and the wet end water chemistry. In order to function effectively and increase paper strength, a dry strength additive must adsorb to the fiber surface and either increase the relative bonded area of the sheet, increase the number of fiber/fiber bonds, and/or increase the strength of those fiber/fiber bonds. The ability of this additive to be effective is therefore dependent on its ability to adsorb to the fiber surface. This can be difficult in some papermaking systems, particularly as more mills recycle their process water and take in less fresh water. This results in high conductivity, fines, and anionic trash, all of which can adsorb to the polymeric strength additive and decrease its effectiveness.

To overcome these challenges, dual component wet end additive programs are sometimes used. These are typically comprised of a cationic and anionic polymer dosed sequentially into the papermaking process, in which the cationic polymer can be used to adsorb to the anionic fiber surface, and the anionic polymer is then added to help retain any excess cationic material. This approach provides a strength improvement relative to single component systems, but it is still subject to the same limitations of all wet end additives; a limited number of fiber surface sites and decreased efficacy due to challenging water chemistry (high conductivity, fines). This approach can also result in decreased sheet formation (high levels of flocculation) due to the interaction between the cationic and anionic additives themselves.

BRIEF SUMMARY

In some embodiments, the present disclosure provides methods for enhancing the strength of a paper sheet. The methods may comprise adding an effective amount of a wet end composition to a furnish comprising a pulp in a wet end of a papermaking process. The wet end composition comprises a cationic polymer or an amphoteric polymer with a net positive charge. The methods comprise forming a paper sheet from the pulp and spraying an effective amount of a composition onto the paper sheet, the composition comprising an anionic polymer comprising amino groups, amide groups, or a combination thereof. At least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde.

In some embodiments, the composition is sprayed onto the sheet prior to a press section.

In some embodiments, the effective amount of the composition and/or the wet end composition is from about 0.05 Ib/ton to about 20 lb/ton, based on dry fiber.

In certain embodiments, the portion comprises from about 10 mole percent to at least about 50 mole percent.

In some embodiments, the amino groups, the amide groups, or the combination of amino groups and amide groups are mono-reacted and di-reacted with the aldehyde at a ratio of mono-reacted to di-reacted of from about 1.1:1 to about 50:1.

In some embodiments, the anionic polymer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-tert-butylacrylamide, N-methylolacrylamide, allylamine, diallylamine, and any combination thereof.

In certain embodiments, the anionic polymer is glyoxalated polyacrylamide.

In some embodiments, the cationic polymer or the amphoteric polymer with the net positive charge comprises acrylamide and a monomer selected from the group consisting of 2-(acryloyloxy)-N,N,N-trimethylethanaminium chloride, diallylamine, diallyldimethylammonium chloride, and any combination thereof.

In some embodiments, the wet end composition comprises hydrolyzed poly(N-vinylformamide) and/or cationic starch, with or without the cationic polymer or the amphoteric polymer with the net positive charge.

The present disclosure also provides methods that may comprise spraying an effective amount of a composition onto the paper sheet, the composition comprising water and an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde, wherein the paper sheet comprises a top ply, a bottom ply, and a filler ply disposed between the top ply and the bottom ply.

The composition may be sprayed to a location selected from the group consisting of a top side of the top ply, a bottom side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof. For example, the composition may be sprayed to a location selected from the group consisting of a top side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.

The effective amount may be from about 0.05 lb/ton to about 20 lb/ton, based on dry fiber.

In some embodiments, the portion comprises from about 10 mole percent to at least about 50 mole percent. The amino groups, the amide groups, or the combination of amino groups and amide groups may be mono-reacted and di-reacted with the aldehyde at a ratio of from about 1.1:1 to about 50:1.

In some embodiments, the composition is sprayed onto the paper sheet prior to a press section.

In some embodiments, the aldehyde is selected from the group consisting of formaldehyde, paraformaldehyde, glyoxal, glutaraldehyde, and any combination thereof.

In some embodiments, the anionic polymer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-tert-butylacrylamide, N-methylolacrylamide, allylamine, diallylamine, and any combination thereof. In some embodiments, the anionic polymer is glyoxalated polyacrylamide.

Additional methods for enhancing the strength of a paper sheet are disclosed herein. In some embodiments, the methods comprise spraying an effective amount of a composition onto the paper sheet, the composition comprising water and an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde, wherein the paper sheet comprises a top ply and a bottom ply, wherein the composition is sprayed at a location selected from the group consisting of a top side of the top ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.

In some embodiments, a filler ply is disposed between the top ply and the bottom ply. The effective amount may be from about 0.05 lb/ton to about 20 lb/ton, based on dry fiber.

In some embodiments, the portion comprises from about 10 mole percent to at least about 50 mole percent. The amino groups, the amide groups, or the combination of amino groups and amide groups may be mono-reacted and di-reacted with the aldehyde at a ratio of from about 1.1:1 to about 50:1.

In some embodiments, the composition is sprayed onto the paper sheet prior to a press section.

The anionic polymer may be, for example, glyoxalated polyacrylamide.

Additional methods for enhancing the strength of a paper sheet are disclosed herein. Such methods may comprise spraying an effective amount of a composition onto the paper sheet, the composition comprising an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde, and wherein the composition is sprayed onto the sheet in a press section or after the press section.

In some embodiments, the paper sheet comprises a top ply, a bottom ply, and a filler ply disposed between the top ply and the bottom ply.

In some embodiments, the composition is sprayed to a location selected from the group consisting of a top side of the top ply, a bottom side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter that form the subject of the claims of this application. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the disclosure as set forth in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:

FIG. 1 shows average strength improvement data from three different cationic wet end polymers;

FIG. 2 shows average strength improvement data from wet end cationic polyacrylamide and wet end cationic starch;

FIG. 3 shows average strength improvement data from multiple wet end additives;

FIG. 4 shows average strength improvement data from wet end cationic polyacrylamide and wet end hydrolyzed poly(N-vinylformamide); and

FIG. 5 shows average strength increase for sheets that were treated with wet end cationic starch (20 lb/ton active) and sprayed with different anionic polymers.

DETAILED DESCRIPTION

Various elements and embodiments of the presently disclosed inventions are described below. The relationship and functioning of the elements of the embodiments may better be understood by reference to the following detailed description. However, it should be understood that embodiments of the presently disclosed inventions are not limited to those explicitly described below.

The present disclosure provides compositions and methods for increasing the strength of paper. The compositions comprise water and one or more anionic polymers, such as anionically-charged aldehyde-functionalized polymers. As used herein, the term “anionic polymer” refers to any polymer having a net negative charge, such as a polymer comprising one or more anionic monomers and optionally one or more monomers that are not anionic, such as nonionic monomers. Additionally, the term “anionic polymer” covers homopolymers, copolymers, terpolymers, etc., having one or more anionic monomers and optionally one or more monomers that are not anionic, such as nonionic monomers. Further, the term “anionic polymer” encompasses amphoteric polymers having a net negative charge.

In some embodiments, the anionic polymers may have from about 1 to about 99 mol % anionic charge. For example, the anionic polymers may have from about 1 to about 90 mol % anionic charge, from about 1 to about 80 mol % anionic charge, from about 1 to about 70 mol % anionic charge, from about 1 to about 60 mol % anionic charge, from about 1 to about 50 mol % anionic charge, from about 1 to about 40 mol % anionic charge, from about 1 to about 30 mol % anionic charge, from about 1 to about 20 mol % anionic charge, from about 1 to about 10 mol % anionic charge, or from about 1 to about 5 mol % anionic charge. In some embodiments, the polymer has about 3 mol % anionic charge, about 4 mol % anionic charge, about 5 mol % anionic charge, about 6 mol % anionic charge, or about 7 mol % anionic charge.

The presently disclosed anionic polymers may also be referred to as “aldehyde-functionalized polymers,” which are polymers that result from a reaction between an aldehyde and a polymer comprising at least one amide group and/or amino group. Representative examples of aldehyde-functionalized polymers are disclosed in, for example, U.S. Pat. No. 7,641,766, U.S. Pat. No. 7,901,543, U.S. Pat. No. 9,951,475, U.S. Pat. No. 9,567,708 and U.S. Pat. No. 10,006,170, the disclosures of which are incorporated by reference into the present application in their entirety.

The amount of water present in the compositions disclosed herein is not particularly limited. In some embodiments, the anionic polymer is in the form of an aqueous composition containing from about 5 to about 15 percent by weight of the polymer. In certain embodiments, the anionic polymer is in the form of an aqueous composition containing from about 5 to about 10 percent by weight of the polymer. In some embodiments, the anionic polymer is in the form of an aqueous composition containing from about 5 to about 8 percent by weight of the polymer. In certain embodiments, the anionic polymer is in the form of an aqueous composition containing about 7, about 7.5, or about 8 percent by weight of the polymer.

Further, the aqueous compositions disclosed in the foregoing paragraph may be subjected to additional dilution with water prior to use. For example, additional water may be added to the aqueous compositions such that the resulting composition comprises water in an amount from about 80 to about 99 percent by weight. In some embodiments, the compositions disclosed herein comprise water in an amount from about 85 to about 99 percent by weight, from about 90 to about 99 percent by weight, or from about 95 to about 99 percent by weight.

The anionic polymers of the present disclosure comprise amino groups, amide groups, or both amino groups and amide groups. One or more of the groups may be substituted with an aldehyde in a mono-reacted to di-reacted ratio of at least about 1.1 to 1. In some embodiments, the ratio may be from at least about 1.2 to 1, at least about 1.3 to 1, at least about 1.4 to 1, at least about 1.5 to 1, at least about 2 to 1, at least about 3 to 1, at least about 4 to 1, at least about 5 to 1, at least about 10 to 1, at least about 15 to 1, at least about 20 to 1, at least about 25 to 1, at least about 30 to 1, at least about 35 to 1, at least about 40 to 1, at least about 45 to 1 or at least about 50 to 1.

In some embodiments, the anionic polymers of the present disclosure comprise amino groups and/or amide groups that are mono-reacted and di-reacted with one or more aldehydes at a ratio of from about 1.1:1 to about 50:1 of mono-reacted to di-reacted. In certain embodiments, the anionic polymers comprise amino groups and/or amide groups that are mono-reacted and di-reacted with one or more aldehydes at a ratio of from about 3:1 to about 50:1, from about 5:1 to about 50:1, from about 10:1 to about 50:1, from about 15:1 to about 50:1, from about 20:1 to about 50:1, from about 25:1 to about 50:1, from about 3:1 to about 20:1, from about 5:1 to about 20:1, or from about 10:1 to about 20:1.

Without wishing to be bound by any particular theory, it is believed that the mono-reacted aldehyde in the polymer may contribute to an enhancement of paper strength. The mono-reacted species (e.g., species having a free aldehyde) may be responsible for a portion of the increase in paper strength because, unlike the di-reacted species, the mono-reacted species can form a covalent bond with cellulose fiber. Therefore, a composition comprising an aldehyde-functionalized polymer having a greater mono- to di-reacted ratio may impart increased strength to paper when added to a papermaking process as compared to an aldehyde-functionalized polymer having an equal or greater di-reacted to mono-reacted ratio.

However, although the mono-reacted species may be responsible for some increase in paper strength, the inventors unexpectedly discovered that a step of spraying the anionic polymer onto a paper sheet imparts a dramatic increase in paper strength above and beyond the increase potentially provided by the mono-reacted species. The effect is even more pronounced when an anionic polymer is sprayed as compared to spraying a cationic or nonionic polymer.

Mono-reacted refers to a polymer formed when one glyoxal unit reacts with one amide or amino group, and di-reacted refers to a polymer formed when one glyoxal unit reacts with two amide or amino groups.

In some embodiments, a portion of the amino groups and/or amide groups is functionalized with one or more aldehydes. In some embodiments, at least about 10 or about 15 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In certain embodiments, at least about 20 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In some embodiments, at least about 25 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In certain embodiments, at least about 30 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In some embodiments, at least about 35 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In certain embodiments, at least about 40 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In some embodiments, at least about 45 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In certain embodiments, at least about 50 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes. In some embodiments, at least about 60, 70, 80 or 90 mole percent of the amino groups and/or amide groups of the anionic polymers are functionalized with one or more aldehydes.

The anionic polymers of the present disclosure may comprise any amount of amino groups and/or amide groups that are mono-reacted. In certain embodiments, at least about 10 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In some embodiments, at least about 15 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In certain embodiments, at least about 20 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In some embodiments, at least about 25 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In certain embodiments, at least about 30 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In some embodiments, at least about 35 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In certain embodiments, at least about 40 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In some embodiments, at least about 45 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In certain embodiments, at least about 50 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde. In some embodiments, at least about 5, 10, 15, 20 or 25 mole percent to about 50, 45, 40, 35 or 30 mole percent of the amino groups and/or amide groups are mono-reacted with at least one aldehyde

The anionic polymers of the present disclosure may be prepared by any suitable synthetic method. For example, a polymer comprising amino groups and/or amide groups may be reacted with an aldehyde at a pH of from about 7 to about 9. An aqueous solution of the polymer comprising amino groups and/or amide groups at a pH of about 9 may be charged with aldehyde at about 25° C. The pH of the solution may be adjusted to a range of from about 7.5 to about 8.5 using a base and the pH may be maintained within that range. Any base may be used, such as sodium or potassium hydroxide. The rate of viscosity increase may be monitored during the reaction using a viscometer. Once the desired viscosity has been reached, such as about 5 cps to about 6 cps, the pH of the reaction mixture may be adjusted to from about 2 to about 3.5 using an acid. Any acid may be used, such as sulfuric acid or hydrochloric acid.

The rate of reaction depends on a variety of factors, such as temperature, total concentration of polymer and aldehyde, ratio of aldehyde to amide/amino functional groups, and pH. Higher reaction rates are expected when the temperature, total concentration of polymer and aldehyde, ratio of aldehyde to amide/amino functional groups, or pH is increased. For example, a higher pH yields a faster increase in viscosity. Therefore, the rate of viscosity can be controlled by increasing or decreasing the pH of the reaction mixture.

In some embodiments, the anionic polymer is synthesized using water-in-oil polymerization (i.e., emulsion), dispersion polymerization, gel polymerization, or solution polymerization methods. In certain embodiments, polyamines and polyamides are prepared by copolymerizing monomers under free radical forming conditions using any of the aforementioned techniques. Polyamines may also be prepared by modification of a pre-formed polyamide, for example, by hydrolysis of an acrylamide-vinylformamide copolymer using acid or base as described in U.S. Pat. Nos. 6,610,209 and 6,426,383, the disclosures of which are incorporated by reference into the present application in their entirety. Polyaminoamides may also be prepared by direct amidation of polyalkyl carboxylic acids and transamidation of copolymers containing carboxylic acid and (meth)acrylamide units (see, for example, U.S. Pat. No. 4,919,821, the disclosure of which is incorporated by reference into the present application in its entirety).

The molecular weight of the resulting anionic polymer is not particularly limited. In some embodiments, the polymerization and/or post polymerization reaction conditions are selected such that the resulting anionic polymer comprising amino and/or amide groups has a weight average molecular weight of from about 1,000 g/mole to about 10,000,000 g/mole. Thus, in certain embodiments, the resulting polymer comprising amino and/or amide groups has a molecular weight of from about 1,000 g/mole to about 5,000,000 g/mole, from about 1,000 g/mole to about 2,000,000 g/mole, from about 1,000 g/mole to about 1,000,000 g/mole, from about 1,000 g/mole to about 500,000 g/mole, from about 1,000 g/mole to about 250,000 g/mole, from about 1,000 g/mole to about 100,000 g/mole, from about 25,000 g/mole to about 1,000,000 g/mole, from about 50,000 g/mole to about 1,000,000 g/mole, from about 100,000 g/mole to about 1,000,000 g/mole, or from about 250,000 g/mole to about 1,000,000 g/mole.

The monomer or monomers used to form the polymer comprising amino groups, amide groups, or a combination of one or more amino groups and one or more amide groups may be nonionic, anionic, or cationic. However, if the polymer is a homopolymer, then the monomer is an anionic monomer.

In some embodiments, the anionic polymer comprises from about 1 to about 99 mole percent of one or more anionic monomers, from about 1 to about 99 mole percent of one or more nonionic monomers, and optionally from about 1 to about 99 mole percent of one or more cationic monomers, provided that if the polymer comprises cationic monomers, the polymer has an overall net negative charge. In some embodiments, the anionic polymer is a copolymer comprising from about 1 to about 50 mole percent of one or more anionic monomers and from about 99 to about 50 mole percent of one or more nonionic monomers. In certain embodiments, the anionic polymer is a copolymer comprising about 1 to about 30 mole percent of one or more anionic monomers and about 99 to about 70 mole percent of one or more nonionic monomers. In some embodiments, the anionic polymer is a copolymer comprising from about 1 to about 99 mole percent of one or more acrylamide monomers and from about 99 mole percent to about 1 mole percent of one or more anionic monomers.

Illustrative, non-limiting examples of nonionic monomers include acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-tert-butylacrylamide, N-methylolacrylamide, diallylamine, allylamine, and the like.

Illustrative, non-limiting examples of anionic monomers include acrylic acid, and its salts, including, but not limited to sodium acrylate, and ammonium acrylate, methacrylic acid, and its salts, including, but not limited to sodium methacrylate, and ammonium methacrylate, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), the sodium salt of AMPS, sodium vinyl sulfonate, styrene sulfonate, maleic acid, and its salts, including, but not limited to the sodium salt, and ammonium salt, sulfonate itaconate, sulfopropyl acrylate or methacrylate or other water-soluble forms of these or other polymerizable carboxylic or sulphonic acids, sulfomethylated acrylamide, allyl sulfonate, sodium vinyl sulfonate, itaconic acid, acrylamidomethylbutanoic acid, fumaric acid, vinylphosphonic acid, vinylsulfonic acid, allylphosphonic acid, phosphonomethylated acrylamide, and the like.

Illustrative, non-limiting examples of cationic monomers include dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, including, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts, such as acrylamidopropyltrimethylammonium chloride, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, methacrylarnidopropyl trimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldiethylammonium chloride, diallyldimethylammonium chloride, and the like. In certain embodiments, the cationic monomer is diallyldimethylammonium chloride.

Additional monomers that can be used in preparation of the polymer include, but are not limited to, N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, 2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine, 2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate, 2-(acryloyloxyethyl)-2′-(trimethylammonium)ethyl phosphate, [(2-acryloylethyl)dimethylammonio]methyl phosphonic acid, 2-methacryloyloxyethyl phosphorylcholine (MPC), 2-[(3-acrylamidopropyl)dimethylammonio]ethyl 2′-isopropyl phosphate (AAPI), 1-vinyl-3-(3-sulfopropyl)imidazolium hydroxide, (2-acryloxyethyl) carboxymethyl methylsulfonium chloride, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, N-(4-sulfobutyl)-N-methyl-N, N-diallylamine ammonium betaine (MDABS), N,N-diallyl-N-methyl-N-(2-sulfoethyl)ammonium betaine, and the like.

In some embodiments, the polymer comprising one or more amino groups, one or more amide groups, or one or more amino and one or more amide groups is formed using at least one vinylic monomer. In certain embodiments, the vinylic monomer is an acrylic monomer. In some embodiments, the polymer comprising amino groups, amide groups, or amino and amide groups comprises an acrylamide monomer or a methacrylamide monomer.

The aldehyde-functionalized polymer and/or the polymer comprising one or more amino groups, one or more amide groups, or one or more amino and one or more amide groups may be a linear, branched, star, block, graft, or dedrimer polymer. Either polymer may be structurally modified using a structural-modifier, such as a cross-linking agent or a chain transfer agent.

Representative cross-linking agents include, but are not limited to, N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, triallylamine, triallyl ammonium salts, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, triethylene glycol dimethylacrylate, polyethylene glycol dimethacrylate, N-vinylacrylamide, N-methylallylacrylamide, glycidyl acrylate, acrolein, glyoxal and vinyltrialkoxysilanes, such as vinyltrimethoxysilane (VTMS), vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, vinyltriacetoxysilane, allyltrimethoxysilane, allyltriacetoxysilane, vinylmethyldimethoxysilane, vinyldimethoxyethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylacetoxysilane, vinylisobutyldimethoxysilane, vinyltriisopropoxysilane, vinyltri-n-butoxysilane, vinyltrisecbutoxysilane, vinyltrihexyloxysilane, vinyltrimethoxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyoctyloxysilane, vinylmethoxydioctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyoxysilane, vinyldimethoxyoleyloxysilane, and the like.

Representative chain transfer agents include, but are not limited to, alcohols, such as methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, and glycerol, and the like, sulfur compounds, such as alkylthiols, thioureas, sulfites, and disulfides, carboxylic acids, such as formic and malic acid, and their salts and phosphites, such as sodium hypophosphite, and combinations thereof.

The aldehyde used to form the anionic polymer / aldehyde-functionalized polymer is not particularly limited. In some embodiments, the aldehyde is selected from the group consisting of formaldehyde, paraformaldehyde, glutaraldehyde, glyoxal, and any combination thereof. In certain embodiments, the aldehyde is glyoxal. In some embodiments, the anionic polymer is formed by reacting a polymer comprising amino and/or amide groups with one aldehyde but in other embodiments, the anionic polymer is formed by reacting a polymer comprising amino and/or amide groups with two or more different aldehydes, three or more different aldehydes, four or more different aldehydes, or five or more different aldehydes.

In some embodiments, the compositions comprise water and a zwitterionic polymer or an amphoteric polymer having a net neutral charge.

The present disclosure also provides wet end compositions that may be added, for example, to the wet end of a papermaking process. In some embodiments, a wet end composition comprises a cationic polymer. For example, the wet end composition may comprise a polymer having one or more cationic monomers. The polymer may also comprise one or more nonionic monomers. Additionally, the polymer may comprise one or more anionic monomers or zwitterionic monomers provided that the polymer has an overall net cationic charge.

In some embodiments, the polymer of the wet end composition comprises from about 0 to about 99 mole percent of one or more anionic monomers, from about 0 to about 99 mole percent of one or more nonionic monomers, from about 0 to about 99 mole percent of one or more zwitterionic monomers and/or from about 1 to about 99 mole percent of one or more cationic monomers, provided that the polymer has an overall net positive charge. In some embodiments, the polymer of the wet end composition comprises from about 1 to about 50 mole percent of one or more cationic monomers and from about 99 to about 50 mole percent of one or more nonionic monomers or other monomers. In certain embodiments, the polymer of the wet end composition comprises about 1 to about 30 mole percent of one or more cationic monomers and about 99 to about 70 mole percent of one or more nonionic monomers or other monomers. In some embodiments, the polymer of the wet end composition comprises from about 1 to about 99 mole percent of one or more acrylamide monomers and from about 99 mole percent to about 1 mole percent of one or more cationic monomers.

For example, the polymer may comprise from about 1 mole percent to about 35 mole percent, from about 1 mole percent to about 30 mole percent, from about 1 mole percent to about 25 mole percent, from about 1 mole percent to about 20 mole percent, from about 1 mole percent to about 15 mole percent, from about 1 mole percent to about 10 mole percent, or from about 1 mole percent to about 5 mole percent of a cationic monomer.

If the polymer is a polyampholyte, it will have a net positive charge. For example, if the polymer comprises about 35 mole percent cationic monomer, it can include from about 1 to 34 mole percent anionic monomer.

Illustrative, non-limiting examples of nonionic monomers include acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-tert-butylacrylamide, N-methylolacrylamide, diallylamine, allylamine, and the like.

Illustrative, non-limiting examples of anionic monomers include acrylic acid, and its salts, including, but not limited to sodium acrylate, and ammonium acrylate, methacrylic acid, and its salts, including, but not limited to sodium methacrylate, and ammonium methacrylate, AMPS, the sodium salt of AMPS, sodium vinyl sulfonate, styrene sulfonate, maleic acid, and its salts, including, but not limited to the sodium salt, and ammonium salt, sulfonate itaconate, sulfopropyl acrylate or methacrylate or other water-soluble forms of these or other polymerizable carboxylic or sulphonic acids, sulfomethylated acrylamide, allyl sulfonate, sodium vinyl sulfonate, itaconic acid, acrylamidomethylbutanoic acid, fumaric acid, vinylphosphonic acid, vinylsulfonic acid, allylphosphonic acid, phosphonomethylated acrylamide, and the like.

Illustrative, non-limiting examples of cationic monomers include dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, including, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts, such as acrylamidopropyltrimethylammonium chloride, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, methacrylarnidopropyl trimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldiethylammonium chloride, diallyldimethylammonium chloride, and the like. In certain embodiments, the cationic monomer is diallyldimethylammonium chloride.

Additional monomers that can be used in preparation of the polymer include, but are not limited to, N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, 2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine, 2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate, 2-(acryloyloxyethyl)-2′-(trimethylammonium)ethyl phosphate, [(2-acryloylethyl)dimethylammonio]methyl phosphonic acid, 2-methacryloyloxyethyl phosphorylcholine (MPC), 2-[(3-acrylamidopropyl)dimethylammonio]ethyl 2′-isopropyl phosphate (AAPI), 1-vinyl-3-(3-sulfopropyl)imidazolium hydroxide, (2-acryloxyethyl) carboxymethyl methylsulfonium chloride, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, N-(4-sulfobutyl)-N-methyl-N, N-diallylamine ammonium betaine (MDABS), N,N-diallyl-N-methyl-N-(2-sulfoethyl)ammonium betaine, and the like.

In some embodiments, the polymer of the wet end composition comprises a nonionic monomer, such as acrylamide, and a cationic monomer, such as any of the cationic monomers disclosed herein. For example, the polymer may comprise from about 1 mol % to about 99 mol % of acrylamide (and/or other nonionic monomer) and from about 99 mol % to about 1 mol % cationic monomer. In some embodiments, the polymer comprises from about 1 mol % to about 35 mol %, from about 1 mol % to about 30 mol %, from about 1 mol % to about 25 mol %, from about 1 mol % to about 20 mol %, from about 1 mol % to about 15 mol %, from about 1 mol % to about 10 mol % or from about 1 mol % to about 5 mol % of cationic monomer.

In some embodiments, the polymer comprises about 10 mol % DMAEA-MCQ (2-(acryloyloxy)-N,N,N-trimethylethanaminium chloride) and about 90 mol % acrylamide. In certain embodiments, the polymer is a cationic diallylamine, such as a polymer comprising about 35 mol % diallylamine and about 65 mol % acrylamide. In some embodiments, the polymer is a cationic GPAM, such as a polymer comprising about 5 mol % DADMAC (diallyldimethylammonium chloride) and about 95 mol % acrylamide.

In some embodiments, the wet end composition is an aqueous composition comprising, for example, water and the polymer comprising one or more cationic monomers disclosed above. In some embodiments, the wet end composition comprises cationic starch and/or partially hydrolyzed poly (N-vinyl formamide).

The amount of water present in the wet end composition disclosed herein is not particularly limited. In some embodiments, the aqueous composition comprises from about 1 to about 50 percent by weight of the polymer, the balance being water and any other additives included in the composition. In certain embodiments, the aqueous composition comprises from about 1 to about 40 percent by weight, from about 1 to about 30 percent by weight, from about 1 to about 20 percent by weight, from about 1 to about 10 percent by weight, or from about 1 to about 5 percent by weight of the polymer.

Further, the aqueous compositions disclosed in the foregoing paragraph may be subjected to additional dilution with water prior to use. For example, additional water may be added to the aqueous compositions such that the resulting composition comprises water in an amount from about 80 to about 99 percent by weight. In some embodiments, the compositions disclosed herein comprise water in an amount from about 85 to about 99 percent by weight, from about 90 to about 99 percent by weight, or from about 95 to about 99 percent by weight.

In some embodiments, a wet end composition may be in the form of a dry powder. In dry form, the powder may comprise, for example, about 90% solids / about 10% water, about 95% solids / about 5% water, or about 100% solids / about 0% water. When the dry powder is used in a papermaking process, it may be dissolved in water such that the water comprises about 1% solids or less. The solids comprise the polymer and/or salts thereof.

The polymer of the wet end composition may be a linear, branched, star, block, graft, or dedrimer polymer. The polymer may be structurally modified using a structural-modifier, such as a cross-linking agent or a chain transfer agent.

The molecular weight of the polymer of the wet end composition is not particularly limited. In some embodiments, the weight average molecular weight is from about 1,000 g/mole to about 10,000,000 g/mole. Thus, in certain embodiments, the polymer has a molecular weight of from about 1,000 g/mole to about 5,000,000 g/mole, from about 1,000 g/mole to about 2,000,000 g/mole, from about 1,000 g/mole to about 1,000,000 g/mole, from about 1,000 g/mole to about 500,000 g/mole, from about 25,000 g/mole to about 3,000,000 g/mole, from about 50,000 g/mole to about 3,000,000 g/mole, from about 100,000 g/mole to about 3,000,000 g/mole, from about 200,000 g/mole to about 3,000,000 g/mole, or from about 250,000 to about 2,000,000 g/mole.

In some embodiments, the wet end composition comprises hydrolyzed poly(N-vinylformamide) and/or cationic starch. The polymer of the wet end composition disclosed above may be present too but also may be excluded. Water and other wet end additives may be present as well.

The present disclosure also provides methods of using the compositions disclosed herein to enhance the strength of paper. In some embodiments, the compositions and methods disclosed herein increase the strength, such as surface strength and/or dry strength, of paper. In some embodiments, the methods comprise spraying a paper sheet with an effective amount of a composition comprising an anionic polymer with amino groups, amide groups, or a combination thereof, as disclosed herein. The composition may be applied/sprayed using a spray boom, spray bar, shower bar, or the like.

The composition may be sprayed onto the top side of the sheet and/or the bottom side of the sheet. If a two-ply sheet is involved, the composition may be sprayed onto the top and/or bottom sides of the top and/or bottom ply. For example, the composition may be sprayed to the top and/or bottom side of the top ply before meshing with the bottom ply. As an additional example, the composition may be sprayed to the top side and/or bottom side of the bottom ply before meshing with the first ply. The composition may be sprayed to either or both sides of the top ply and/or the bottom ply before and/or after meshing together. Further, there may be one or more plies in between the top ply and bottom ply. Such plies may be referred to as filler plies. The composition may also be sprayed to a top side and/or bottom side of the filler ply before meshing with the top and/or bottom ply.

In some embodiments, the paper sheet comprises a top ply, a bottom ply, and a filler ply disposed between the top ply and the bottom ply. The composition may be sprayed to a location selected from the group consisting of a top side of the top ply, a bottom side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof. In certain embodiments, the composition is sprayed to a location selected from the group consisting of a top side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.

In some embodiments, the paper sheet comprises a top ply and a bottom ply. The composition may be sprayed at a location selected from the group consisting of a top side of the top ply, a bottom side of the top ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.

After the anionic polymers disclosed herein are sprayed onto the paper sheet, the paper sheet may be subjected to additional rounds of spraying. In the subsequent rounds of spraying, additional anionic polymer may be sprayed and/or hydrolyzed poly(N-vinylformamide) may be sprayed. The hydrolyzed poly(N-vinylformamide) may be a component in an aqueous composition. In some embodiments, the sheet may be subsequently sprayed with a 0.01 N NaOH solution.

The location of the spray boom may vary and the size is not particularly limited. For example, the wet end of a papermaking machine may include a headbox, which contains the furnish. The headbox distributes the furnish onto a wire where the water from the furnish is drained. The spray boom may be located in a position downstream of the headbox such that it can spray the composition onto the pulp/sheet as it forms on the and/or after it has formed on the wire. The spray boom may be located before a press section, in the press section, after the press section, and any combination thereof. If multiple spray booms are present, each spray boom may be located prior to the press section, in the press section, or after the press section. Further, zero, one or more spray booms may be located prior to the press section, zero, one or more spray booms may be located in the press section, and zero, one or more spray booms may be located after the press section.

In some embodiments, the spray boom may be about as wide as the sheet being formed. In certain embodiments, the spray boom may be from about 20 inches wide to about 300 inches wide, such as about 30 inches, about 50 inches, about 100 inches, about 150 inches, about 200 inches, about 250 inches, or about 300 inches wide. One or more spray booms may be located at any position along the wire. The wire transports the sheet to the press section of the papermaking machine. One or more spray booms may be located at any point between the headbox and the press section. Additionally or alternatively, one or more spray booms may be located in the press section or after the press scetion.

The effective amount of anionic polymer added to the paper sheet is not limited. In certain embodiments, a composition comprising one or more anionic polymers is added to the paper sheet in an effective amount of about 0.05 lb/ton to about 20 lb/ton, based on dry fiber. For example, the effective amount may be from about 0.05 lb/ton to about 18 lb/ton, from about 0.05 lb/ton to about 15 lb/ton, from about 0.05 lb/ton to about 12 lb/ton, from about 0.05 lb/ton to about 10 lb/ton, from about 0.05 lb/ton to about 8 lb/ton, from about 0.05 lb/ton to about 6 lb/ton, from about 0.05 lb/ton to about 4 lb/ton, from about 0.05 lb/ton to about 3 lb/ton, from about 0.15 lb/ton to about 2 lb/ton, from about 1 lb/ton to about 20 lb/ton, from about 1 lb/ton to about 18 lb/ton, from about 1 lb/ton to about 15 lb/ton, from about 2 lb/ton to about 20 lb/ton, from about 2 lb/ton to about 18 lb/ton, from about 2 lb/ton to about 15 lb/ton, from about 5 lb/ton to about 15 lb/ton, from about 1 lb/ton to about 10 lb/ton, from about 1 lb/ton to about 5 lb/ton, from about 1 lb/ton to about 3 lb/ton, or from about 0.5 lb/ton to about 3 lb/ton. In certain embodiments, a composition comprising one or more anionic polymers is added to the paper sheet in an amount from about 0.05 lb/ton to about 3 lb/ton.

Conventional microparticles, alum, cationic starch or a combination thereof may be utilized as adjuncts with the anionic polymer treatment, though it should be emphasized that no adjunct is required. In some embodiments, a composition disclosed herein may comprise water, an anionic polymer, and starch.

The anionic polymers disclosed herein are useful for strengthening all grades of paper and paperboard. In some embodiments, the anionic polymers are used to prepare recycle board grades using OCC (old corrugated containers), with or without mixed waste. In some embodiments, the anionic polymers are used to prepare virgin, recycled, mechanical, chemical, bleached, or unbleached paper.

In some embodiments, when using the presently disclosed anionic polymers, optional methods of fixing the polymer to the fiber may be employed. The “fixing” is typically accomplished by using cationic materials in conjunction with the polymers. For example, the cationic materials may be added to the furnish in the wet end. Such cationic materials are most frequently coagulants, either inorganic (e.g., alum, polyaluminum chlorides, iron chloride or sulfate, and any other cationic hydrolyzing salt) or organic (e.g., p-DADMACs, EPI/DMAs, PEIs, modified PEIs or any other high charged density low to medium molecular weight polymers). Additionally, cationic materials added for other purposes, such as starch, wet strength, or retention additives, can also serve to fix the anionic polymer.

In some embodiments, the methods disclosed herein include an additional step of adding a wet end composition to the wet end of a papermaking process, such as to the thin and/or thick stock. Significantly enhanced strength, such as dry strength, can be achieved by adding a wet end composition to the wet end, forming a sheet, and spraying a composition comprising an anionic polymer to the resulting sheet at a location such as before a press section. These method steps result in the unexpected finding that a chemical interaction can occur between the sprayed additives and the wet end additives, and the resulting strength is greater than the sum of each individual additive. The inventors discovered that the sprayed polymer additive interacts with the wet end polymer additive to form a polymer network, which results in an unexpected strength, such as dry strength, improvement.

In some embodiments, a wet end composition comprising a cationic polymer (or amphoteric polymer having a net positive charge) is added to the wet end of the paper machine and the sprayed anionic polymers are applied to the semi-wet sheet after the head box but before the press section.

The effective amount of cationic polymer or amphoteric polymer with a net positive charge added to the wet end is not limited. In certain embodiments, a wet end composition comprising the cationic and/or amphoteric polymer is added to the paper sheet in an effective amount of about 0.05 lb/ton to about 20 lb/ton, based on dry fiber. For example, the effective amount may be from about 0.05 lb/ton to about 18 lb/ton, from about 0.05 lb/ton to about 15 lb/ton, from about 0.05 lb/ton to about 12 lb/ton, from about 0.05 lb/ton to about 10 lb/ton, from about 0.05 lb/ton to about 8 lb/ton, from about 0.05 lb/ton to about 6 lb/ton, from about 0.05 lb/ton to about 4 lb/ton, from about 0.05 lb/ton to about 3 lb/ton, from about 0.15 lb/ton to about 2 lb/ton, from about 1 lb/ton to about 20 lb/ton, from about 1 lb/ton to about 18 lb/ton, from about 1 lb/ton to about 15 lb/ton, from about 2 lb/ton to about 20 lb/ton, from about 2 lb/ton to about 18 lb/ton, from about 2 lb/ton to about 15 lb/ton, from about 5 lb/ton to about 15 lb/ton, from about 1 lb/ton to about 10 lb/ton, from about 1 lb/ton to about 5 lb/ton, from about 1 lb/ton to about 3 lb/ton, or from about 0.5 lb/ton to about 3 lb/ton. In certain embodiments, a wet end composition comprising the cationic and/or amphoteric polymer is added to the wet end in an amount from about 0.05 lb/ton to about 3 lb/ton.

Additionally, traditional wet end additives can be added to the wet end in combination with the methods disclosed herein. Such additives include, but are not limited to, retention aids, strength additives, sizing agents, and the like.

The compositions and methods of the present disclosure can be used in any papermaking process, including in a method of making paper products from pulp, comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet and drying the sheet. The steps of forming the papermaking furnish, draining, and drying the sheet may be carried out in any conventional manner generally known to those skilled in the art.

The present disclosure also covers paper sheets produced according to any of the methods disclosed herein.

The following examples further illustrate aspects of the present disclosure but should not be construed in any way to limit the scope of the present disclosure.

EXAMPLES

The following examples show the unexpected paper strength results achieved in connection with the inventions disclosed in the present application. The examples also show the criticality of spraying the compositions disclosed herein as well as the criticality of spraying polymers having a net negative charge. Further, the examples show the unexpected synergy discovered by utilizing a method including the steps of adding a wet end composition comprising a cationic polymer to the wet end, forming a paper sheet, and spraying the polymers having the net negative charge to the paper sheet.

The strengthening effects of the presently disclosed anionic polymers were evaluated through paper machine trials. Compositions comprising the anionic or cationic polymers were applied to the paper sheet on the wire using a spray boom at a location between the headbox and the press section.

In a first trial, a composition comprising water and anionic glyoxalated polyacrylamide (aGPAM) was sprayed onto the sheet before it entered the press section but after water from the furnish was drained. The molecular weight of the polymer was about 500,000 Da. The composition was sprayed in an amount of about 1 lb aGPAM per ton of dry fiber. The sheet then traveled through the press section and drying section to the reel section. The portion of the sheet that was sprayed with the aGPAM was cut from the reel and divided into eight different segments. Each segment was subjected to a scuff test, which is a test where the sheet is rubbed or abraded until the sheet begins to break. A higher scuff value indicates a stronger surface strength. The results are shown in Table 1.

TABLE 1 Test 1 215 Test 2 328 Test 3 35 Test 4 236 Test 5 47 Test 6 40 Test 7 29 Test 8 49

The average scuff value for the eight tests was about 122.

In a second trial, the same procedure as the first trial was used except that the composition was sprayed in an amount of about 0.5 lb aGPAM per ton of dry fiber. Results are shown in Table 2.

TABLE 2 Test 1 80 Test 2 38 Test 3 89 Test 4 149 Test 5 32 Test 6 47 Test 7 27 Test 8 36

The average scuff value for the eight tests was about 62.

In a third trial, the same procedure as the first trial was used except that the composition was sprayed in an amount of about 1 lb cationic GPAM per ton of dry fiber. Results are shown in Table 3.

TABLE 3 Test 1 40 Test 2 46 Test 3 27 Test 4 28 Test 5 43 Test 6 34 Test 7 35 Test 8 17

The average scuff value for the eight tests was about 34.

In a fourth trial, the same procedure as the first trial was used except that the composition was sprayed in an amount of about 3 lb cationic GPAM per ton of dry fiber. Results are shown in Table 4.

TABLE 4 Test 1 17 Test 2 21 Test 3 68 Test 4 40 Test 5 78 Test 6 25 Test 7 63 Test 8 48

The average scuff value for the eight tests was about 45.

In a fifth trial (conducted in substantially the same manner as the first trial), water (with no polymer) was sprayed onto the sheet and the average scuff value was about 17. This indicates that paper strength can be increased by over 7 times by adding the anionic polymer.

Further, when the dosage of aGPAM was doubled from 0.5 lb/ton to 1 lb/ton, the scuff value about doubled as well. However, when the dosage of the cationic GPAM was tripled from 1 lb/ton to 3 lb/ton, the scuff value did not triple and did not even double.

Additionally, while using only half as much aGPAM as compared to cationic GPAM (compare Tables 2 and 3), the scuff value for the aGPAM was about double. When comparing 1 lb/ton aGPAM against 1 lb/ton cationic GPAM, the scuff value is almost 4 times higher.

In additional trials, the inventors compared spraying aGPAM onto a paper sheet versus adding aGPAM to the furnish in the wet end.

With respect to the wet end trial, the inventors added about 21 lb/ton starch to the wet end and no aGPAM was added. The sheet was formed, transported through the papermaking machine, and a sample was cut and subjected to a scuff test. A scuff value of about 15 was achieved.

Next, the same process was carried out but this time, about 0.7 lb/ton of the aGPAM was added to the wet end in addition to the starch. A scuff value of about about 17 was achieved, which was only 2 points higher than the trial without aGPAM addition.

Finally, about 1.4 lb/ton aGPAM was sprayed onto the sheet before it entered the press section and about 12 lb/ton starch was added in the wet end. The resulting sheet achieved a scuff value of about 31. Although the dosage sprayed was about double the dosage added to the wet end in the first trial, the amount of starch was almost cut in half and the scuff value still almost doubled when the aGPAM was sprayed as compared to when it was added to the wet end.

The inventors surprisingly and unexpectedly discovered that spraying the presently disclosed anionic polymers onto the paper sheet dramatically increased the resulting strength of the paper sheet as compared to other methods of applying the anionic polymers to the sheet. Not only did the inventors unexpectedly discover the significant benefits resulting from spraying the anionic polymer, the inventors also unexpectedly discovered that the dramatic increase in strength is only achieved by spraying anionic polymers as compared to other polymers, such as nonionic polymers and cationic polymers.

In additional trials, the present inventors also discovered synergy between additives added to the wet end and additives sprayed onto the paper sheet. To further explore this effect, several different wet end additives were used in combination with spraying aGPAM. FIG. 1 shows the sheet strength of several different cationic wet end additives of different chemical structure, with and without aGPAM applied as a spray. Each wet end additive was dosed at about 6 lb/ton actives. The bar graph on the left-hand side in each column represents wet end treatment only (no spray) and the bar graph on the right-hand side in each column represents wet end treatment and spray treatment (about 6 lb/ton anionic GPAM). Each one shows an increase in strength with aGPAM spray.

FIG. 2 shows that wet end cationic starch can also be used to induce a strengthening effect with the aGPAM spray. The cationic polyacrylamide was added at about 8 lb/ton and the starch was added at about 20 lb/ton. The bar graph on the left-hand side in each column represents wet end treatment only (no spray) and the bar graph on the right-hand side in each column represents wet end treatment and spray treatment (about 8 lb/ton anionic GPAM).

FIG. 3 shows that polyacrylamide-based polyampholytes can be used to induce a strengthening effect with the aGPAM spray (with the exception of net anionic polyampholytes). Each wet end additive was dosed at about 8 lb/ton, the polyaluminum chloride (PAC) was present at about 10 lb/ton product, and the alum was present at about 20 lb/ton. The bar graph on the left-hand side in each column represents wet end treatment only (no spray) and the bar graph on the right-hand side in each column represents wet end treatment and spray treatment (about 8 lb/ton anionic GPAM).

A study was also carried out using hydrolyzed poly(N-vinylformamide) (pNVF) in the wet end. The pNVF polymer, which contained primary amine groups, had a pre-hydrolysis molecular weight of about 640 kDa and a degree of hydrolysis of about 88%. FIG. 4 shows the strength data of wet end pNVF and a cationic polyacrylamide sample, each dosed at about 8 lb/ton). Sheets containing each wet end additive were sprayed with a low and high mono-AcAm aGPAM (about 8 lb/ton). The graph on the left-hand side of each column represents strength from the wet end additive alone (no spray). The graph on the right-hand side of each column represents strength with the wet end additive plus spraying the low mono-AcAm and the graph in the middle of each column represents strength with the wet end additive plus spraying the high mono-AcAm. The strength results show that the high mono-AcAm aGPAM spray produces higher strength than the low mono-AcAm. The aGPAM-sprayed sheets containing the pNVF wet end additive show higher strength than those containing the cPAM wet end additive (despite the lower baseline strength of pNVF sheets).

An additional study was carried out using sprayed anionic polymers that contained no aldehyde groups. Cationic starch (about 20 lb/ton) was added to the wet end. The data is shown in FIG. 5 . The dotted line indicates the strength from the wet end starch alone. The bar graphs dropping below 0.00% show the strength due to each sprayed polymer only. The bar graphs rising above 0.00% indicate the strength from sheets that contain wet end starch and sprayed polymer. The polymers tested were anionic polyacrylamide polymers having about 5 mol % acrylic acid and about 95 mol % acrylamide. Sample ID 7401-056 had an intrinsic viscosity of about 2.48, a Huggins constant of about 0.24 and a weight average molecular weight of about 660 kDa. Sample ID 7401-063 had an intrinsic viscosity of about 2.38, a Huggins constant of about 0.45 and a weight average molecular weight of about 760 kDa. Sample ID 7401-065 had an intrinsic viscosity of about 3.38, a Huggins constant of about 0.36 and a weight average molecular weight of about 1,600 kDa. Sample ID 7537-155 had an intrinsic viscosity of about 0.73, a Huggins constant of about 0.2 and a weight average molecular weight of about 100 kDa. It was found that no anionic polyacrylamide polymer was able to induce a strengthening effect. The aGPAM polymer was the only sprayed anionic polymer found to induce a strength response, indicating an importance of the aldehyde group.

These examples show that significantly enhanced paper strength can be achieved using the methods and compositions disclosed and claimed herein. Further, the results demonstrate the unexpected finding that a chemical interaction can occur between the sprayed additives and the wet end additives, and the resulting strength is greater than the sum of each individual component.

All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. In addition, unless expressly stated to the contrary, use of the term “a” is intended to include “at least one” or “one or more.” For example, “a polymer” is intended to include “at least one polymer” or “one or more polymers.”

Any ranges given either in absolute terms or in approximate terms are intended to encompass both, and any definitions used herein are intended to be clarifying and not limiting. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges (including all fractional and whole values) subsumed therein.

Any composition disclosed herein may comprise, consist of, or consist essentially of any element, component and/or ingredient disclosed herein or any combination of two or more of the elements, components or ingredients disclosed herein.

Any method disclosed herein may comprise, consist of, or consist essentially of any method step disclosed herein or any combination of two or more of the method steps disclosed herein.

The transitional phrase “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, un-recited elements, components, ingredients and/or method steps.

The transitional phrase “consisting of” excludes any element, component, ingredient, and/or method step not specified in the claim.

The transitional phrase “consisting essentially of” limits the scope of a claim to the specified elements, components, ingredients and/or steps, as well as those that do not materially affect the basic and novel characteristic(s) of the claimed invention.

Unless specified otherwise, all molecular weights referred to herein are weight average molecular weights and all viscosities were measured at 25° C. with neat (not diluted) polymers.

As used herein, the term “about” refers to the cited value being within the errors arising from the standard deviation found in their respective testing measurements, and if those errors cannot be determined, then “about” may refer to, for example, within 5% of the cited value.

Furthermore, the invention encompasses any and all possible combinations of some or all of the various embodiments described herein. It should also be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. 

What is claimed is:
 1. A method for enhancing the strength of a paper sheet, comprising: adding an effective amount of a wet end composition to a furnish comprising a pulp in a wet end of a papermaking process, wherein the wet end composition comprises a cationic polymer or an amphoteric polymer with a net positive charge, forming a paper sheet from the pulp, and spraying an effective amount of a composition onto the paper sheet, the composition comprising an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde.
 2. The method of claim 1, wherein the composition is sprayed onto the sheet prior to a press section.
 3. The method of claim 1, wherein the effective amount of the composition and/or the wet end composition is from about 0.05 lb/ton to about 20 lb/ton, based on dry fiber.
 4. The method of claim 1, wherein the portion comprises from about 10 mole percent to at least about 50 mole percent.
 5. The method of claim 1, wherein the amino groups, the amide groups, or the combination of amino groups and amide groups are mono-reacted and di-reacted with the aldehyde at a ratio of mono-reacted to di-reacted of from about 1.1:1 to about 50:1.
 6. The method of claim 1, wherein the anionic polymer comprises a monomer selected from the group consisting of acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-tert-butylacrylamide, N-methylolacrylamide, allylamine, diallylamine, and any combination thereof.
 7. The method of claim 1, wherein the anionic polymer is glyoxalated polyacrylamide.
 8. The method of claim 1, wherein the cationic polymer or the amphoteric polymer with the net positive charge comprises acrylamide and a monomer selected from the group consisting of 2-(acryloyloxy)-N,N,N-trimethylethanaminium chloride, diallylamine, diallyldimethylammonium chloride, and any combination thereof.
 9. The method of claim 1,wherein the wet end composition comprises hydrolyzed poly(N-vinylformamide) and/or cationic starch.
 10. A method for enhancing the strength of a paper sheet, comprising: spraying an effective amount of a composition onto the paper sheet, the composition comprising water and an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde, wherein the paper sheet comprises a top ply, a bottom ply, and a filler ply disposed between the top ply and the bottom ply.
 11. The method of claim 10, wherein the composition is sprayed to a location selected from the group consisting of a top side of the top ply, a bottom side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.
 12. The method of claim 10, wherein the composition is sprayed to a location selected from the group consisting of a top side of the top ply, a top side of the filler ply, a bottom side of the filler ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof. 13-14. (canceled)
 15. The method of claim 10, wherein the amino groups, the amide groups, or the combination of amino groups and amide groups are mono-reacted and di-reacted with the aldehyde at a ratio of mono-reacted to di-reacted of from about 1.1:1 to about 50:1.
 16. The method of claim 10, wherein the composition is sprayed onto the paper sheet prior to a press section. 17-19. (canceled)
 20. A method for enhancing the strength of a paper sheet, comprising: spraying an effective amount of a composition onto the paper sheet, the composition comprising water and an anionic polymer comprising amino groups, amide groups, or a combination thereof, wherein at least a portion of the amino groups and/or the amide groups are functionalized with an aldehyde, wherein the paper sheet comprises a top ply and a bottom ply, wherein the composition is sprayed at a location selected from the group consisting of a top side of the top ply, a top side of the bottom ply, a bottom side of the bottom ply, and any combination thereof.
 21. The method of claim 20, wherein a filler ply is disposed between the top ply and the bottom ply.
 22. The method of claim 20, wherein the effective amount is from about 0.05 lb/ton to about 20 lb/ton, based on dry fiber.
 23. The method of claim 20, wherein the portion comprises from about 10 mole percent to at least about 50 mole percent.
 24. The method of claim 20, wherein the amino groups, the amide groups, or the combination of amino groups and amide groups are mono-reacted and di-reacted with the aldehyde at a ratio of mono-reacted to di-reacted of from about 1.1:1 to about 50:1.
 25. The method of claim 20, wherein the composition is sprayed onto the paper sheet prior to a press section. 26-29. (canceled) 